1. Field of the Invention
The invention relates to the removal of free fatty acid from used frying fat and oils, for example in commercial fast food restaurants where large amounts of frying fat and oils are used in food preparation. In particular, the invention relates to the use of a dry cyclodextrin/absorbent mixture that is reacted with the used frying fat or oil under low heat, followed by a slight reduction in temperature and the addition of a small amount of water to aid agglomeration. This is followed by filtration to separate the agglomerated cyclodextrin/absorbent and free fatty acid from the frying fat or oil.
2. Prior Art
It has long been known that frying fat and cooking oils tend to decompose to some extent with use thereby forming fatty acids in the fat and/or oil. The presence of free fatty acids in used frying fat and edible oils leads to undesirable properties and degradation of their frying properties. Such undesirable properties include but are not necessarily limited to excessive smoke formulation at higher cooking temperatures and a tendency of the frying fats and cooking oils with even small amounts of free fatty acid to foam or boil while cooking. These undesirable properties make used frying fats and oils more difficult to work with due to the presence of the excessive smoke and the increased risk of burns resulting from the spattering of the foaming or boiling frying fat or oil.
Further, the presence of free fatty acids in used frying fats and oils degrades their frying properties causing the foods fried in such fats and oils to often become too browned on the outside before the food is properly cooked on the inside. The presence of free fatty acids also causes used frying fats and oils to have oleophilic properties with food which often leaves oily residues on the surface of fried foods prepared in used frying fats and oils.
Skilled practitioners in this art have tried numerous different approaches to find an inexpensive method to purify used frying fats and oils and remove the free fatty acids which are largely responsible for the undesirable and degraded frying properties associated with the use of used frying fats and oils. For example, edible glyceride oils have been conventionally refined by alkali treatment such as with an aqueous solution of sodium hydroxide. The alkali treatment neutralizes the free fatty acids by forming soaps. In U.S. Pat. No. 3,008,972 oils having a high free fatty acid content are treated with a sodium hydroxide and concentrated diammonium phosphate solution. In Japanese Patent 5532 (1954) refined oils of high free fatty acid content were suspended in strong ethanol solutions before being treated with alkali to purify the oils.
A problem with the use of alkali treatments to remove free fatty acids, however, is that the free fatty acids are neutralized by forming soaps, which are in themselves an undesirable byproduct. Further, when free fatty acids are removed by alkali treatments some neutral oil is often lost by entrainment or occlusion in the soap that is formed.
Another prior art approach to the problem of purifying used frying fats and oils has been to use treating agents such as clays, magnesium silicates, zeolites, activated aluminas and charcoal. U.S. Pat. No. 4,735,815 and U.S. Pat. No. 4,701,438, for example, disclose the purification of used frying oils; and fats by contacting the oils and fats with a treating composition of an acid activated clay or a magnesium silicate and gel-derived alumina. For example, the acid activated clay may be a bentonite activated with sulfuric acid. The magnesium silicate may either be natural, such as talc or serpentine, or synthesized such as by the interaction of a magnesium salt and a soluble silicate. The gel-derived alumina suitable for use in the treating composition has a pseudoboehmite content of at least 20% by weight. The disadvantage of using such a treatment composition, however, is that purification of the fats and oils takes place at controlled elevated temperatures within the temperature range from about: 120.degree. C. to about 190.degree. C. Lower temperatures affect the efficiency of the treatment, while higher temperatures may cause the oils or fats to further degrade, thus causing losses.
Another approach to reducing the free fatty acid content of edible oils disclosed in U.S. Pat. No. 3,491,132 is to purify, the oils by using a clyclodextrin to form a clathrate with free fatty acids and then remove the clathrated clyclodextrin and fatty acids. This approach, however, is disclosed as a means of initial purification for oils with exceptionally high free fatty acid content, i.e., essentially those with more than about 5% and as high as 10 to 20% free acid content. Due to their very high free fatty acid content, these crude oils are often considered unrefinable due to the large neutral oil losses that are incurred during conventional refining of such oils. However as disclosed in U.S. Pat. No. 3,491,132, cyclodextrin may be used in an initial refining process to reduce the undesirably high free fatty acid content of, e.g. about 10 to 20%, to lower workable levels of, e.g., below about 5%. Once the free fatty acid content of such oils is reduced to below about 5%, further free fatty acid removal may thereafter be efficiently accomplished by conventional means, such as by alkali treatment.
In addition to the disadvantage of requiring a subsequent further conventional refining step or process such as alkali treatment with its associated disadvantages, the method disclosed in U.S. Pat. No. 3,491,132 also suffers from the disadvantages that the disclosed process requires a significant quantity of water for clathration and very large amounts of cyclodextrin in relation to the amount of oil to be purified. In general, for this method about equal amounts of the oil and cyclodextrin are mixed with water in an amount equal to about one-half of the amount of the oil to be purified.
U.S. Pat. No. 4,330,564 discloses a process for treating used fryer cooking oil at an elevated temperature of from about 300.degree. F. to about 400.COPYRGT.F. (about 149.degree. C. to about 204.degree. C.) with a composition of water, food compatible acid such as citric, tartaric or phosphoric acid, and a porous carrier such as porous rhyolite or perlite. The carrier must have sufficient porosity to absorb the water and release it when the composition is contacted with the hot oil. The high temperature of the oil during treatment causes steaming and releasing of the water from the porous carrier and food compatible acid in the composition. This steaming is relied upon to cause jet-propelled dispersal of the composition throughout the oil to allow good contact between the treating composition and the oil. Once the treatment is competed, the residue of the composition is removed by hot filtering the oil. As with other prior art methods discussed, this method of removal of fatty acids also has the disadvantages that it must be carried out at elevated temperatures and requires a significant quantity of water to effect dispersion of the food compatible acid and absorbent in the oil.
Another prior art approach to purifying used frying fat and oil relates to processes that use filtering media. U.S. Pat. No. 4,764,384 is exemplary of such processes. It discloses the use of a filtering media containing synthetic amorphous silica with absorbed moisture, synthetic amorphous magnesium silicate, diatomaceous earth and synthetic amorphous silica-alumina. This filtering media is mixed with the used frying fat or cooking oil at an elevated temperature of about 275.degree. F. (135.degree. C.) to form a slurry. According to this process, the most effective absorption action is produced when the cooking oil and filtering media are hot, such as at about 275.degree. F. After about five (5) minutes of contact, the hot slurry is passed through a paper filter thereby trapping the filtering media and other contaminants and allowing the purified oil to pass through the paper filter to a container. As with other prior art approaches, this method also suffers from disadvantages associated with purifying used frying fats and oils at elevated temperatures.
In view of the disadvantageous of the prior art approaches, it would be very desirable to provide a method of removing free fatty acid from used frying fats and oils that overcomes these disadvantages. In particular, it would be desirable to provide a method of removing free fatty acid from used frying fats and oils that does not have to be carried out at excessive elevated temperatures and that does not require significant quantities of water and/or other compositions in relation to the amount of used frying tat or oil from which the free fatty acid is to be removed.
Thus there exists a need to formulate a method of removing free fatty acids from used frying fats and oils that can be carried out at relatively low temperatures compared to prior art processes, and therefore more safely with reduced risk of burns. There also exists a need to formulate a method of removing free fatty acids from frying fats and oils that can be carried out without the use of significant quantities of water and/or other compositions in relation to the amount of used frying fat or oil to be purified.